Methods for forming a corrosion-protective coating layer on a metal surface generally include a hot coating method which is carried out on the production line and a cold coating method which is carried out on the work site.
The hot coating method employs a lining of a molten polyethylene resin, a molten epoxy resin or the like. This method, however, suffers from several disadvantages, i.e. the lining is complicated, a large amount of heat capacity is required, the lining tends to be damaged during storage or transportation, and it is difficult to form the lining on pipeline joints.
On the other hand, the cold coating method, which uses a polymerization-curable polyurethane resin or epoxy resin having a film-forming ability, is also disadvantageous is that it is difficult to obtain a uniform coating. Further, in the case where a two-part system is used, the resulting coating tends to have uneven properties due to the variation of the mixing ratio.
Another method is known where protective material in the form of tape or sheet with a pressure-sensitive adhesive layer formed on one side thereof is wound around or stuck to the metal surface. This method is advantageous because a coating layer of uniform thickness can be formed by a simple press-bonding means. However, this methed is disadvantageous because the cohesive force of the adhesive layer is comparatively low, and formation of wrinkles and lifting arise due to the ambient temperature or soil pressure.